The present application is generally directed to nanoscale computing and memory circuits, and, more particularly, to the formation of wires for device applications, specifically, use of imprinting to form electrodes, devices, and circuits. By xe2x80x9cnanoscalexe2x80x9d is meant that either the vertical dimension or the electrical pathway between electrodes is measured in nanometers.
With the constantly decreasing feature sizes of integrated-circuit devices, well-behaved devices are becoming increasingly difficult to design. The fabrication is also becoming increasingly difficult and expensive. In addition, the number of electrons either accessed or utilized within a device is decreasing, with increasing statistical fluctuations in the electrical properties. In the limit, device operation depends on a single electron, and traditional device concepts must change.
Molecular electronics has the potential to augment or even replace conventional devices with electronic elements, can be altered by externally applied voltages, and have the potential to scale from micron-size dimensions to nanometer-scale dimensions with little change in the device concept. The molecular switching elements can be formed by inexpensive solution techniques; see, e.g., C. P. Collier et al, xe2x80x9cElectronically Configurable Molecular-Based Logic Gatesxe2x80x9d, Science, Vol. 285, pp. 391-394 (Jul. 16, 1999) and C. P. Collier et al, xe2x80x9cA [2]Catenane-Based Solid State Electronically Reconfigurable Switchxe2x80x9d, Science, Vol. 289, pp. 1172-1175 (Aug. 18, 2000). The self-assembled switching elements may be integrated on top of a Si integrated circuit so that they can be driven by conventional Si electronics in the underlying substrate. To address the switching elements, interconnections or wires are used.
Molecular electronic devices, comprising crossed wire switches, hold promise for future electronic and computational devices. Thin single or multiple atomic layers can be formed, for example, by Langmuir-Blodgett techniques or self-assembled monolayer on a specific site. A very controlled roughness of the underlying surface is needed to allow optimal LB film formation. A crossed wire switch may comprise two wires, or electrodes, for example, with a molecular switching species between the two electrodes.
For nanoscale electronic circuits, it is necessary to invent new materials with the functions envisioned for them and new processes to fabricate them. Nanoscale molecules with special functions can be used as basic elements for nanoscale computing and memory applications.
As an example, imprinting techniques have been developed for nanometer-scale patterned thin films; see, e.g., S. Y. Chou et al, xe2x80x9cImprint Lithography with 25-Nanometer Resolutionxe2x80x9d, Science, Vol. 272, pp. 85-87 (Apr. 5, 1996) and U.S. Pat. No. 5,772,905, entitled xe2x80x9cNanoimprint Technologyxe2x80x9d, issued on Jun. 30, 1998, to S. Y. Chou, both of which are incorporated herein by reference.
Briefly, the imprinting method comprises compression molding and a pattern transfer process. In imprint lithography, a mold with nanometer-scale features is first pressed into a thin resist cast on a substrate, which creates a thickness contrast pattern in the resist. After the mold is removed, an anisotropic etching process is used to transfer the pattern into the entire resist thickness by removing the remaining resist in the compressed areas.
A need exists to incorporate the imprinting method in fabricating nanoscale circuits suitable for industrial fabrication processes.
In accordance with the present invention, a method of fabricating a molecular electronic device is provided. The molecular electronic device comprises at least one pair of crossed wires and a molecular switch film therebetween, wherein each pair of crossed wires and the molecular switch film form an electrochemical cell. The method comprises:
(a) forming at least one bottom electrode on a substrate by first forming a first layer on the substrate and patterning the first layer to form the bottom electrode by an imprinting technique;
(b) forming the molecular switch film on top of the bottom electrode;
(c) forming a protective layer on top of the molecular switch film to avoid damage thereto during further processing;
(d) coating a polymer layer on top of the protective layer and patterned the polymer layer by the imprinting method to form openings that expose portions of the protective layer; and
(e) forming at least one top electrode on the protective layer through the openings in the polymer layer by first forming a second layer on the polymer layer and patterning the second layer.
The imprinting method, as employed herein, can be used to fabricate nanoscale patterns over a large area at high speeds acceptable in industrial standards. Consequently, it can be used to fabricate nanoscale molecular devices, e.g., crossbar memory circuits.